Recently, image formation of an electrophotographic system, using a toner for electrostatic image development (hereinafter, also denoted simply as a toner) can perform full-color printing as well as mono-chromatic printing, as typified by conventional document preparation. Such a full-color image forming apparatus, which can prepare prints of the number of required sheets for on-demand printing without making any printing plate, has become mainly employed in the field of short-run printing, as described in, for example, JP-A No. 2005-15724 (hereinafter, the JP-A refers to Japanese Patent Application Publication).
When preparing full-color prints of catalogs or for advertisement using a toner, the toner used therein requires color reproducibility to obtain an image faithful to the original image. Namely, in full-color image formation, toner images of yellow, magenta and cyan are superimposed to reproduce the targeted color image and such color toners on which attainment of faithful color reproduction is based are required to achieve superior color reproducibility.
Recently, there have been increased opportunities to form graphic images on the display by a computer to output the image. The color gamut in conventional color printing or color photographic system is much narrower than that formed on the display so that outputting the image on the display as such on paper or the like has been limited in photographic prints for personal use or in commercial printing. Thus, a toner capable of expanding the color gamut can also achieve expanded color gamut, so that it was highlighted as a problem to be overcome to make it feasible to output prints with a color gamut close to that of the display.
Based on the foregoing background, there have been studied various colorants aimed to achieve enhanced color reproducibility.
There are included, for example, copper phthalocyanine pigments as one of typical cyan colorants used for color toners. Toners using such copper phthalocyanine pigments are versatile and exhibit superior light stability but result in an increased base line on the longer wavelength side of a reflection spectrum of the image and tend to form color images with slight color contamination. Therefore, such copper phthalocyanine pigments have been regarded not to be suitable for image formation demanding high color reproduction, as typified by prints of company logos.
Accordingly, there was studied development of a toner not causing color contamination by improving copper phthalocyanine pigments, as described in, for example, JP-A No. 5-239368, but which did not achieve sufficient reduction of color contamination.
Toners using pigments such as a copper phthalocyanine pigment exhibit versatility achieving image quality at the level of images prepared in printing inks but were difficult to attain a hue angle suited for color reproduction of photographic images. Accordingly, there were studied toners containing a colorant capable of achieving a hue angle suitable for color reproduction of a photographic image, as described in, for example, JP-A Nos. 5-239368 and 2006-63171.